Process of making zinc base alloys



Dec. 27, 1955 c. J. TOBIN 2,728,657

PROCESS OF MAKING ZINC BASE LLOYS lFiled Sept. 25,' 1950 Sheets-Sheet l msx. 0.45am 0.4515' amas. (1457,, om; dao/xs, 0.607,5] dans: dans) @507.51 aan n'. man. amm 0.457211" aman" 119mm. aoam aloznn aso n aaoznn 090ml BH @www 7075? Dec. 27, 1955 c. J. ToBlN 2,728,657

PROCESS OF MAKING ZINC BASE ALLOYS Filed Sept. 25, 1950 2 Sheets-Shee'c 2 :inventor Zim Gttornegs United States Patent O PROCESS F MAKING ZINC BASE ALLOYS Clarence J. Tobin, Detroit, Mich., assgnor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application September 25, 1950, Serial No. 186,534

2 Claims. (Cl. 75178) The present invention relates to an improved alloy for glrlawing dies and to a process for producing such an In the forming of metal shapes from sheet metal where the final form of the part requires a substantial amount of metal deformation, as, for example, in the forming of the various contoured parts of the body assembly of automotive vehicles, it is common practice to use drawing dies of cast iron or steel. Such dies are especially resistant to Wear and while expensive, are used extensively in the automotive industry where large quantities of a shaped part are formed. Where, however, the part may not be required in large numbers, the initial expense of cast iron or steel drawing dies is prohibitive. Accordingly, there has been considerable demand for a material having suitable characteristics for drawing dies and less expensive in initial costs. An alloy which has found extensive use in the aircraft industry as a drawing die alloy for forming shaped parts from aluminum is the zinc base alloy containing copper, aluminum and magnesium and commonly known as Kirksite. Where such dies have been used to make shaped metal parts from metals other than aluminum they have not been entirely satisfactory.

Accordingly, it is an object of the present invention to provide an improved zinc base alloy for drawing dies.

It is another object of the present invention to provide a low cost zinc base drawing die alloy. Y

It is still another object to provide a process for making such a zinc base alloy.

The alloy and the process for making the same which I desire to protect herein are specified with particularity in the appended claims and are described in the following specication. The drawings comprise Figures 1, 2, 3 and 4 illustrating macrographic views of the alloy of the present invention and Figures 5 and 6 illustrate in a cross-sectional view and a perspective view a typical drawing die made from such an alloy.

In accordance with one aspect of the present invention an exceptional combination of strength and wear resistance is obtained in zinc base alloys for drawing dies by controlled additions of silicon or silicon with manganese.

I have found that the controlled addition of silicon or silicon with manganese to a zinc base alloy containing aluminum, copper, magnesium with the balance zinc provides a dispersion of hard particles within the alloy which makes it particularly wear-resistant and especially suitable for use in drawing dies. In this connection it is believed that the desirable wear-resistance properties result from the formation of hard particles of silicon or an inter-metallic compound of manganese and silicon.

The addition of silicon alone to a zinc base alloy of the above composition will produce hard particles in the matrix which improves its wear-resisting properties to a considerable degree. In this connection it is believed that these particles are substantially pure silicon containing not more than a minor percentage of other metals in solution as impurities. As metallic silicon can be added Patented Dec. 21, 1955 to the zinc rich alloy only with considerable difficulty because of the low solubility of silicon' in solid and liquid zinc, it is preferably added as a hardening alloy of aluminum-silicon. The molten zinc will dissolve the aluminum from the hardening alloy and reject the silicon, leaving the silicon in the molten zinc as solid hard particles. Because these particles of solid substantially pure silicon present in the zinc rich base alloy have a substantially lower specific gravity than the zinc rich molten alloy they tend to float to the surface of the molten alloy and a heterogeneous material results.

With the addition of manganese to the zinc base alloy containing silicon, the manganese combines with the silicon to form hard particles of substantially higher specific gravity than the pure silicon particles, and consequently the tendency for oating and separation of the hard particles is lessened. Further, manganese when present with silicon in the zinc base alloy has no detrimental effect on the wear-resistance of the alloy. Its desirable function appears to be in obtaining a more suitable distribution of the hard-particles in the molten alloy prior to solidication. I have found that it is preferable to add the manganese to the zinc in the form of a copper-manganese alloy hardener.

The silicon may also be added to the zinc rich molten alloy asa copper-silicon alloy hardener. However, in adding the silicon in this manner the dissociation of the copper from the silicon by solution of the copper in the zinc'is not complete and the remaining copper-silicon particles do not provide the wear-resisting characteristics obtained by the addition of silicon alone or in the form of the aluminum-silicon alloy hardener.

The zinc base alloys which I have found to have an exceptional combination of strength and wear-resistance in drawing dies contain substantially .2 to 1.2% silicon, 2.0 to 4.5% aluminum, .5 to 4.0% copper, .05 to .25% magnesium with the balance substantially all zinc. As pointed out heretofore, a more desirable dispersion of the hard particles is obtained when the above alloy contains substantially .l to 1.2% manganese. The alloys which I have found preferable for drawing die alloys contain .45

to .75% silicon, .45 to .90% manganese, 2.0 to 4.5% aluminum, .5 to 4.0% copper, .05 to 25% magnesium with the balance substantially all zinc. Optimum characteristics of castability, strength and wear-resistance are obtained with alloys containing .45% silicon, .70% manganese, 2.75 to 3.50% copper, 3.75 to 4.25% aluminum and .05 to .25% magnesium.

The forming of the drawing die alloy of the present invention may be accomplished in ditferentmanners. However, I have found that improved characteristics are obtained where as a rst step commercially pure Zinc or mixtures of commercially pure zinc and scrap alloy of the Kirksite type are mixed together and melted in a separate furnace.

The temperature of the molten material is brought to a temperature of 825 to 875 degrees Fahrenheit while at the same time a copper-manganese alloy hardener is melted in a separate furnace and brought to a temperature of substantially 1750 to 2000 degrees Fahrenheit. The molten alloy hardener is then added to the molten zinc or zinc andV Kirksite mixture. At this stage I have found it desirable to remove any dross that is formed at the surface of the melt. This is accomplished by the addition of a ilux such, for example, as ammonium chloride. The addition of the ammonium chloride reduces the metal oxides and leaves a resultant ash or dross which is skimmed from the surface. With the melting of the zinc or zinc and scrap Kirksite alloy and the coppermanganese alloy hardener a second hardening alloy of aluminum-silicon is melted in still another furnace and brought to a temperature of 1300 to 1500 degrees Fahrenheit. The second alloy hardener is subsequently added to the; molten. mixture orAV zine' oir zinc and scrap Kirksite alloy and the copper manganesehardeningalloy.. EinalLy.,.

magnesium in the form of rods, bars or ingots is added by submerging it below the surface of the bath and allowing.; it' to dissolve.. Constant; agitation't of:v the molten 'mix-l ture: is desirable. during allof; the alloyingfoperations4 and intheladle:before'casting:

Where the' melting; of the alloy.- is initiated; withlcorn`- mercially'pure zinc. and:- a'dditionsof: serapralloy of the- Kirksite-,typeit will be..appreciated.that'ithechemicalcom# positionsA of. the. alloyhardeners-willbe adjusted to obg tain. the. desired composition: inA thenali product. Inthisconnection itv might be. added` that when:- scrapfnretal isi used the; best resultsl are obtainedlby.' limiting theiscrap metal to 50% by weight ofthe'initial rne'lto scrap metal' and; commercially' purev zinc;

The: alloyy is. cast .into drawing. die'. shapes*` preferably ini green sand'. open. moldsv throught gates: whichA enter the mold.y ne'a'r: the. bottom. Heat: is"-A applied to: theexposed' liquidi metal-l surface, so that; the" metal willi solidify: from the. bottom. offthe` castingupwardly.; "Ilo compensate for. shrinkage,.molten metal isladdedtozthe topof thecasting` asshrinkageoccurs dnring'solidication. Toavoidior rei duce'- segregaton of: thehard particles during casting iti.

hasV been found'` desirable to. heat the 'molten'. metal to av temperature of substantially 775 31825.degreesFahrem` ciently freer'ow ofthe molten liquid.` to prevent uneven.

shrinkage and warping in the casting.

I'n the drawings-the macrographieviews of Figures-i4,

5 and 6 illustrate the dispersion of the hard? particleslof."

silicon or thelintermetalliclcompound:of silicon andL man@ ganese in the zine richmatrix.

Alloys suchas I5 have described have unusual characteristics 1 of strength and wear-resistance.which1 make; them: particularly useful and d'esirableffor.` drawing; die'aalloysin: drawingI die operations Where: thezinitial` expense4 of; castl iron orsteel drawing diesis prohibitive..

WhatIiclaimanddesire to secure by: Letters Patent of the UnitedStates is;

11. The' processl of making alldrawingfdieof azincibaser alloy characterized by a high degree of wear-resistance and. consisting essentiallyv of* .5 to.l 4.0% copper, 2-.0- to` 4.5% aluminum, .2 to 1.2%. silicon, 1.0 to 1.2% manganese, .05 to .25% magnesium with the balance zinc which comprises as the rst step heating Zinc to a tcmperature of substantially 825 to 875 degrees F., adding thereto a copper-manganese. alloy which has been heated to substantially 1750 to 2000 degrees F., adding thereto an aluminum-silicon alloy which-hasbeen lieated'to' substantially 1300 to.15.00 degrees F.. andthereaiter adding magnesium. and castingsaid Zinc base alloy ati a temperature of'substantially l0 to 15 degrees F. abovezits melting temperature.

2; The process of'v making a drawing` die of' a Vhighly wear-resistant zincbase alloy.V characterized by a dispersion therein of hard particles of an intermctallic cornpound of manganese and silicon and consisting essentially of approximately 2% to 4.5% aluminum, 0.5% to 4% copper; 0.05% to 0.215%' magnesium; 0.2% to 1.2% silicon, 031% to1.2% manganese' and the balance zinc plus incidental impurities, said process comprising the steps of mel'ting'zinc,l aluminum and" copper-together and heating toat'ernperature of' approximately825` to 875 degrees F., addih'gftheretoa moltenV copper-manganese alloy heated to-axtemperature ofv about 1750 t'o' 2000 degrees F., subsequently adding) a moltenA aluminum-silicon' alloy heated toa4 temperature-4 of 1-300 to-1500 degrees F., thereafter adding magnesium, andv finally castinggthe molten metal at1 a'` temperature of approximately 10 to 15' degrees F. abovetlie meltingtemperature ofv theresultant' zinc base alloy.'

References Cited: inthef le of this patentv UNIT ED= STATES` PATENTS 1,596,761" Peirce et al; Aug. 17, 1926 1,815,479 M'orrellv July 2l', 1931 FOREIGN PATENTS 411,557w Great Britain June l2, 1934 420,672 Great Britain Nov. 30, 1934 429,021 Great. Britain May 2l, l35 351,744 Italy. Aug, 20, '1937 5222724 Great Britain IuneZS, l940 OTHER REFERENCES' Iron Age, Aug. 3, 1944, pages 4649; 132,134.l

Malware-...v A 

1. THE PROCESS OF MAKING A DRAWING DIE OF A ZINC BASE ALLOY CHARACTERIZED BY A HIGH DEGREE OF WATER-RESISTANCE AND CONSISTING ESSENTIALLY OF .5 TO 4.0% COPPER, 2.0 TO 4.5% ALUMINUM, .2 TO 12% SILICON, 1.0 TO 1.2% MANGANESE, .05 TO .25% MAGNESIUM WITH THE BALANCE ZINC WHICH COMPRISES AS THE FIRST STEP HEATING ZINC TO A TEMPERATURE OF SUBSTANTIALLY 825 TO 875 DEGREES, F., ADDING THERETO A COPPER-MANGANESE ALLOY WHICH HAS BEEN HEATED TO SUBSTANTIALLY 1750 TO 2000 DEGREES F., ADDING THERETO AN ALUMNIUM-SILICON ALLOY WHICH HAS BEEN HEATED TO SUBSTANTIALLY 1300 TO 1500 DEGREES F. AND THEREAFTER ADDING MAGNESIUM AND CASTING SAID ZINC BASE ALLOY AT A TEMPERATURE OF SUBSTANTIALLY 10 TO 15 DEGREES F. ABOVE ITS MELTING TEMPERATURE. 